Heterogeneity of carotenoid content and composition in LH2 of the purple sulphur bacterium Allochromatium minutissimum grown under carotenoid-biosynthesis inhibition

The Adaptive Role of Carotenoids and Anthocyanins in Solanum lycopersicum Pigment Mutants under High Irradiance

The effects of high-intensity light on the pigment content, photosynthetic rate, and fluorescence parameters of photosystem II in high-pigment tomato mutants (hp 3005) and low-pigment mutants (lp 3617) were investigated. This study also evaluated the dry weight percentage of low molecular weight antioxidant capacity, expression patterns of some photoreceptor-regulated genes, and structural aspects of leaf mesophyll cells. The 3005 mutant displayed increased levels of photosynthetic pigments and anthocyanins, whereas the 3617 mutant demonstrated a heightened content of ultraviolet-absorbing pigments. The photosynthetic rate, photosystem II activity, antioxidant capacity, and carotenoid content were most pronounced in the high-pigment mutant after 72 h exposure to intense light. This mutant also exhibited an increase in leaf thickness and water content when exposed to high-intensity light, suggesting superior physiological adaptability and reduced photoinhibition. Our findings indicate that the enhanced adaptability of the high-pigment mutant might be attributed to increased flavonoid and carotenoid contents, leading to augmented expression of key genes associated with pigment synthesis and light regulation.

Effect of Light of Different Spectral Compositions on Pro/Antioxidant Status, Content of Some Pigments and Secondary Metabolites and Expression of Related Genes in Scots Pine

The aim of this study was to investigate the effect of light quality (white fluorescent light, WFL, containing UV components), red light (RL, 660 nm), blue light (BL, 450 nm), and white LED light (WL, 450 + 580 nm) on the components of the cellular antioxidant system in Pinus sylvestris L. in needles, roots, and hypocotyls, focusing on the accumulation of key secondary metabolites and the expression of related genes. The qualitative and quantitative composition of carotenoids; the content of the main photosynthetic pigments, phenolic compounds, flavonoids (catechins, proanthocyanidins, anthocyanins), ascorbate, and glutathione; the activity of the main antioxidant enzymes; the content of hydrogen peroxide; and the intensity of lipid peroxidation (MDA and 4-HNE contents) were determined. RL resulted in an increase in the content of hydrogen peroxide and 4-HNE, as well as the total fraction of flavonoids in the needles. It also enhanced the expression of several PR (pathogen-related) genes compared to BL and WL. WFL increased the content of phenols, including flavonoids, and enhanced the overall activity of low-molecular antioxidants in needles and hypocotyls. BL increased the content of ascorbate and glutathione, including reduced glutathione, in the needles and simultaneously decreased the activity of peroxidases. Thus, by modifying the light quality, it is possible to regulate the accumulation of secondary metabolites in pine roots and needles, thereby influencing their resistance to various biotic and abiotic stressors.

Effect of high-intensity light on the photosynthetic activity, pigment content and expression of light-dependent genes of photomorphogenetic Solanum lycopersicum hp mutants

The relationship between photosynthesis, pigment accumulation, and the expression of key light-regulated genes in Solanum lycopersicum hp-1, hp-2 and hp-1.2 photomorphogenetic mutants under conditions of high-intensity light (2000 μm (photons) m^-2s^-1) was studied. The hp-2 mutant (LA3006) and the hp-1 mutants (LA4012 and LA3538) are deficient in DET1 (De-etiolated 1 and DDB1 (DNA DAMAGE-BINDING PROTEIN 1), respectively, which are components of the CDD complex (COP10, DDB1, DET1). HP mutants are superproducers of various pigments and are sensitive to light. We have shown that HIL (high-intensity light) causes a decrease in PSII activity after 24 and 72 h of irradiation, which was partially restored after 72 h in the WT. The photosynthetic rate noticeably decreased only in LA4012 and LA3538 after 24 h of irradiation. After 72 h, the photosynthetic rate decreased in all mutants, with the exception of hp-1.2 LA0279, but the decrease was most noticeable in LA4012, yet significant changes in the respiration rate were absent. The LA0279 mutant was more capable of accumulating anthocyanin in the cells of the subepidermal parenchyma and chlorenchyma, as well as in the cells at the base of large multicellular glandular trichomes and in the mesophyll. Another important difference was the accumulation of increased amounts of antheraxanthin and phenolic compounds in the leaves of LA0279 after 72 h of HIL irradiation. Unlike LA4012, LA3006, LA0279, and LA3538 sowed a significant increase in the expression levels of CHS, HY5, and FLS genes after 24 h, which may be one of the reasons for the higher adaptive potential of those three mutants. In addition to that in LA3538, strong light-induced stress led to an increased level of flavonol synthase (FLS) expression in the LA3006, LA0279, and LA4012 mutants. We hypothesize that the photosynthetic apparatus (PA) of the LA0279 mutant, which is deficient in the DET1 and DDB1 genes, is most adapted to prolonged HIL. Most likely, the resistance of PA mutants to HIL is due to a variety of factors, which, in addition to the redistribution of carotenoids, may include morphological features associated with the accumulation of anthocyanin in the epidermis, subepidermal layer, mesophyll and trichomes of leaves and with an increase in leaf thickness.

Carotenoids Do Not Protect Bacteriochlorophylls in Isolated Light-Harvesting LH2 Complexes of Photosynthetic Bacteria from Destructive Interactions with Singlet Oxygen

The effect of singlet oxygen on light-harvesting (LH) complexes has been studied for a number of sulfur (S+) and nonsulfur (S-) photosynthetic bacteria. The visible/near-IR absorption spectra of the standard LH2 complexes (B800-850) of Allochromatium (Alc.) vinosum (S+), Rhodobacter (Rba.) sphaeroides (S-), Rhodoblastus (Rbl.) acidophilus (S-), and Rhodopseudomonas (Rps.) palustris (S-), two types LH2/LH3 (B800-850 and B800-830) of Thiorhodospira (T.) sibirica (S+), and an unusual LH2 complex (B800-827) of Marichromatium (Mch.) purpuratum (S+) or the LH1 complex from Rhodospirillum (Rsp.) rubrum (S-) were measured in aqueous buffer suspensions in the presence of singlet oxygen generated by the illumination of the dye Rose Bengal (RB). The content of carotenoids in the samples was determined using HPLC analysis. The LH2 complex of Alc. vinosum and T. sibirica with a reduced content of carotenoids was obtained from cells grown in the presence of diphenylamine (DPA), and LH complexes were obtained from the carotenoidless mutant of Rba. sphaeroides R26.1 and Rps. rubrum G9. We found that LH2 complexes containing a complete set of carotenoids were quite resistant to the destructive action of singlet oxygen in the case of Rba. sphaeroides and Mch. purpuratum. Complexes of other bacteria were much less stable, which can be judged by a strong irreversible decrease in the bacteriochlorophyll (BChl) absorption bands (at 850 or 830 nm, respectively) for sulfur bacteria and absorption bands (at 850 and 800 nm) for nonsulfur bacteria. Simultaneously, we observe the appearance of the oxidized product 3-acetyl-chlorophyll (AcChl) absorbing near 700 nm. Moreover, a decrease in the amount of carotenoids enhanced the spectral stability to the action of singlet oxygen of the LH2 and LH3 complexes from sulfur bacteria and kept it at the same level as in the control samples for carotenoidless mutants of nonsulfur bacteria. These results are discussed in terms of the current hypothesis on the protective functions of carotenoids in bacterial photosynthesis. We suggest that the ability of carotenoids to quench singlet oxygen (well-established in vitro) is not well realized in photosynthetic bacteria. We compared the oxidation of BChl850 in LH2 complexes of sulfur bacteria under the action of singlet oxygen (in the presence of 50 μM RB) or blue light absorbed by carotenoids. These processes are very similar: {[BChl + (RB or carotenoid) + light] + O2} → AcChl. We speculate that carotenoids are capable of generating singlet oxygen when illuminated. The mechanism of this process is not yet clear.

Effects of glycine on cell growth and pigment biosynthesis in Rhodobacter azotoformans

The effect of exogenous glycine (a precursor for the biosynthesis of bacteriochlorophyll) on the cell growth and photopigment accumulation was investigated in phototrophic growing Rhodobacter azotoformans 134K20. The growth rate and the biomass of strain 134K20 were significantly inhibited by glycine addition when ammonium sulfate or glutamate were used as nitrogen sources and acetate or succinate as carbon sources. A characteristic absorption maximum at approximately 423 nm was present in the absorption spectra of glutamate cultures while it was absent by the addition of high-concentration glycine of 15 mM. The component account for the 423 nm peak was eventually identified as magnesium protoporphyrin IX monomethyl ester, a precursor of bacteriochlorophyll a (BChl a). Comparative analysis of pigment composition revealed that the amount of BChl a precursors was significantly decreased by the addition of 15-mM glycine while the BChl a accumulation was increased. Moreover, glycine changed the carotenoid compositions and stimulated the accumulation of spheroidene. The A₈₅₀ /A₈₇₅ in the growth-inhibited cultures was increased, indicating an increased level of the light-harvesting complex 2 compared to the reaction center. The exogenous glycine possibly played an important regulation role in photosynthesis of purple bacteria.

The LH2 Complexes (B800-850 and B800-830) Are Assembled in the Cells of the Sulfur Bacterium Thiorhodospira sibirica Strain Kir-3 without Carotenoids

The results of assembling the light-harvesting complexes in the cells of the purple sulfur bacterium Thiorhodospira (T.) sibirica strain Kir-3 while suppressing the biosynthesis of carotenoids with diphenylamine (DPA) were studied. LH2 complexes (B800-850 and B800-830) with different carotenoid composition were isolated from the cells obtained. Maximum inhibition of carotenoid biosynthesis (~90% of the control) was reached at an inhibitor concentration of 53.25 μM (9 mg/L). It was established that changes in the qualitative and quantitative composition of carotenoids do not affect the assembly of B800-830 and B800-850 complexes. It is assumed that, in the population of DPA-LH2 complexes from T. sibirica strain Kir-3, both the carotenoidless complexes and the complexes containing one or two carotenoid molecules can be assembled. These results support the hypothesis that carotenoids are not required for assembling B800-850 and B800-830 complexes.

Bacteriochlorophyll Interaction with Singlet Oxygen in Membranes of Purple Photosynthetic Bacteria: Does the Protective Function of Carotenoids Exist?

The direct action of singlet oxygen on the bacteriochlorophyll (BChl) of light-harvesting complexes in the membranes of four species of purple non-sulfur and sulfur photosynthesizing bacteria with and without carotenoids was studied. It was found that BChl in carotenoidless samples is generally more resistant to the action of singlet oxygen compared to the control. It is assumed that carotenoids are not required to protect BChl of bacterial light-harvesting complexes from singlet oxygen, and in the classic work by Griffith et al. [1] the apoptosis process in carotenoidless mutant cells, which involves the destruction of complexes, the appearance of monomeric BChl, and the generation of singlet oxygen caused by BChl, followed by BChl oxidation, was mistakenly attributed to the protective function of carotenoids.

Excitation energy transfer from the bacteriochlorophyll Soret band to carotenoids in the LH2 light-harvesting complex from Ectothiorhodospira haloalkaliphila is negligible

Pathways of intramolecular conversion and intermolecular electronic excitation energy transfer (EET) in the photosynthetic apparatus of purple bacteria remain subject to debate. Here we experimentally tested the possibility of EET from the bacteriochlorophyll (BChl) Soret band to the singlet S₂ level of carotenoids using femtosecond pump-probe measurements and steady-state fluorescence excitation and absorption measurements in the near-ultraviolet and visible spectral ranges. The efficiency of EET from the Soret band of BChl to S₂ of the carotenoids in light-harvesting complex LH2 from the purple bacterium Ectothiorhodospira haloalkaliphila appeared not to exceed a few percent.

Distribution of rhodopin and spirilloxanthin between LH1 and LH2 complexes when incorporating carotenoid mixture into the membrane of purple sulfur bacterium Allochromatium minutissimum in vitro

Carotenoid mixture enriched by rhodopin and spirilloxanthin was incorporated in LH2 and LH1 complexes from Allochromatium (Alc.) minutissimum in vitro. The maximum incorporating level was ~95%. Rhodopin (56.4%) and spirilloxanthin (13.8%) were incorporated into the LH1 complex, in contrast to the control complex, which contained primarily spirilloxanthin (66.8%). After incorporating, the LH2 complex contained rhodopin (66.7%) and didehydrorhodopin (14.6%), which was close to their content in the control (67.4 and 20.5%, respectively). Thus, it was shown that carotenoids from the total pool are not selectively incorporated into LH2 and LH1 complexes in vitro in the proportion corresponding to the carotenoid content in the complexes in vivo.

Characterisation of the LH2 spectral variants produced by the photosynthetic purple sulphur bacterium Allochromatium vinosum

This study systematically investigated the different types of LH2 produced by Allochromatium (Alc.) vinosum, a photosynthetic purple sulphur bacterium, in response to variations in growth conditions. Three different spectral forms of LH2 were isolated and purified, the B800-820, B800-840 and B800-850 LH2 types, all of which exhibit an unusual split 800 peak in their low temperature absorption spectra. However, it is likely that more forms are also present. Relatively more B800-820 and B800-840 are produced under low light conditions, while relatively more B800-850 is produced under high light conditions. Polypeptide compositions of the three different LH2 types were determined by a combination of HPLC and TOF/MS. The B800-820, B800-840 and B800-850 LH2 types all have a heterogeneous polypeptide composition, containing multiple types of both α and β polypeptides, and differ in their precise polypeptide composition. They all have a mixed carotenoid composition, containing carotenoids of the spirilloxanthin series. In all cases the most abundant carotenoid is rhodopin; however, there is a shift towards carotenoids with a higher conjugation number in LH2 complexes produced under low light conditions. CD spectroscopy, together with the polypeptide analysis, demonstrates that these Alc. vinosum LH2 complexes are more closely related to the LH2 complex from Phs. molischianum than they are to the LH2 complexes from Rps. acidophila.

The LH2 complexes are assembled in the cells of purple sulfur bacterium Ectothiorhodospira haloalkaliphila with inhibition of carotenoid biosynthesis

The effect of the inhibitor of carotenoid (Car) biosynthesis, diphenylamine (DPA), on the cells of the purple sulfur bacterium Ectothiorhodospira (Ect.) haloalkaliphila has been studied. There occurs an inhibition of the biosynthesis of colored Cars (≥99 %) at 71 μM DPA. Considering "empty" Car pockets (Moskalenko and Makhneva 2012) the content of Cars in the DPA-treated samples is first calculated more correctly. The total content of the colored Cars in the sample at 71 μM DPA does not exceed 1 % of the wild type. In the DPA-treated cells (membranes) a complete set of pigment-protein complexes is retained. The LH2 complex at 71 μM DPA is isolated, which is identical to the LH2 complex of the wild type in near IR absorption spectra. This suggests that the principles for assembling this LH2 complex in vivo in the absence of colored Cars remain the same. These results are in full agreement with the data obtained earlier for Allochromatium (Alc.) minutissimum (Moskalenko and Makhneva 2012). They are as follows: (1) DPA almost entirely inhibits the biosynthesis of the colored Cars in Ect. haloalkaliphila cells. (2) In the DPA-treated samples non-colored Cars are detected at 53.25 μM DPA (as traces) and at 71 μM DPA. (3) DPA may affect both phytoene synthase (at ≤71 μM DPA) and phytoene desaturase (at ≥53.25 μM DPA). (4) The assembly of LH2 complex does occur without any colored Cars.

Coupling of different isolated photosynthetic light harvesting complexes and CdSe/ZnS nanocrystals via Förster resonance energy transfer

The present work describes results obtained on hybrid systems formed in aqueous buffer solution by self-assembly of different CdSe quantum dots (QDs) surrounded by a ZnS shell and functionalized by covering the surface with anionic and cationic groups and various isolated pigment-protein complexes from the light-harvesting antennae of photosynthetic organisms (light-harvesting complexes 1 and 2 (LH1 and LH2, respectively) from purple bacteria, phycobiliproteins (PBPs) from cyanobacteria and the rod-shaped PBP from the cyanobacterium Acaryochloris marina). Excitation energy transfer (EET) from QDs to PBP rods was found to take place with varying and highly temperature-dependent efficiencies of up to 90%. Experiments performed at room temperature on hybrid systems with different QDs show that no straightforward correlation exists between the efficiency of EET and the parameter J/(R(12)(6)) given by the theory of Förster resonance energy transfer (FRET), where J is the overlap integral of the normalized QD emission and PBP absorption and R(12) the distance between the transition dipole moments of donor and acceptor. The results show that the hybrid systems cannot be described as randomly orientated aggregates consisting of QDs and photosynthetic pigment-protein complexes. Specific structural parameters are inferred to play an essential role. The mode of binding and coupling seems to change with the size of QDs and with temperature. Efficient EET and fluorescence enhancement of the acceptor was observed at particular stoichiometric ratios between QDs and trimeric phycoerythrin (PE). At higher concentrations of PE, a quenching of its fluorescence is observed in the presence of QDs. This effect is explained by the existence of additional quenching channels in aggregates formed within hybrid systems. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum

The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N=11) and spirilloxanthin (N=13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N=13) to play the role of the direct quencher of the excited singlet state of BChl.

Two-photon excitation spectroscopy of carotenoid-containing and carotenoid-depleted LH2 complexes from purple bacteria

We applied two-photon fluorescence excitation spectroscopy to LH2 complex from purple bacteria Allochromatium minutissimum and Rhodobacter sphaeroides . Bacteriochlorophyll fluorescence was measured under two-photon excitation of the samples within the 1200-1500 nm region. Spectra were obtained for both carotenoid-containing and -depleted complexes of each bacterium to allow their direct comparison. The depletion of carotenoids did not alter the two-photon excitation spectra of either bacteria. The spectra featured a wide excitation band around 1350 nm (2x675 nm, 14,800 cm(-1)) which strongly resembled two-photon fluorescence excitation spectra of similar complexes published by other authors. We consider obtained experimental data to be evidence of direct two-photon excitation of bacteriochlorophyll excitonic states in this spectral region.